The present development is a multistage process for converting solid hydrocarbon resources, such as coal, oil shale and biomass, into synthetic oil. Raw hydrocarbon material is initially treated in a pre-heater and dryer system. The treated material is then subjected to pyrolysis conditions. The raw liquids generated by the pyrolysis conditions are then exposed to upgrading conditions to isolate the desired synthetic oil.
The Department of Energy and other commercial entities have expressed an interest in identifying ways to product marketable hydrocarbon liquids, such as synthetic oil, from coal, oil shale and biomass. However, this has not yet been accomplished at affordable cost.
There are basically two methods for extracting synthetic liquids from hydrocarbon resources: liquefaction and pyrolysis. Liquefaction, a process which converts solid mass to liquid hydrocarbon, requires relatively high reaction temperatures and pressures. Pyrolysis, a process which strips valuable liquid hydrocarbon from a solid but leaves a solid residue or char, can operate at more moderate temperatures and lower pressures, such as atmospheric pressure. Thus, although liquefaction produces more of the desired liquid hydrocarbon than pyrolysis, the reaction conditions make liquefaction a high cost operation.
In the prior art, attempts have been made to improve liquefaction processes. For example, the processing material may be pretreated, or the processing material may be mixed with oils which are expected to serve as hydrogen donors during processing, or the material may be processed in a hydrogen-rich atmosphere under elevated pressure. These processing variations have increased the yield and quality of the synthetic liquids produced, but at high operating costs because of the need for expensive equipment and large energy consumption.
Similarly, the prior art cites attempts to improve pyrolysis processes. In particular, there is a need to improve yield, quality—the resultant oil often contains dust and ash—and to eliminate or reduce the number of carbon deposits formed during operation. It is known that the material to be processed can be heated with hot recycled ash or by partial combustion of some of the hydrocarbon material. However, the hot ash is very active and when used for heating raw material to pyrolysis temperature some of the vaporized synthetic oil is carbonized on the ash, thereby reducing the yield of hydrocarbon liquids. When partial combustion is used for heating, the product gases of combustion, primarily nitrogen, carbon dioxide, water vapor and carbon monoxide, dilute the desired hydrocarbon product vapors, thereby requiring costly separation stages.
The present development addresses the problems presented by the liquefaction and the pyrolysis processes by using standard boiler-type designs for handling large amounts of hydrocarbon material to produce very large quantities of synthetic hydrocarbon liquids at affordable prices.